Adjustable voltage autotransformer



April 4, 1967 R. G. EDGERLY, JR., ETAL 3,312,921

ADJUSTABLE VOLTAGE AUTOTRANSFORMER Filed May 10, 1965 INVENTOR5 Raymond G. Figarlgi BY New "War? Zure LZ United States Patent ADJUSTABLE VOLTAGE AUTOTRANSFORMER Raymond G. Edgerly, Jr., andNorman K. Zurell, Bristol, Conn., assignorsto The Superior Electric Company, Bristol, Conn., a corporation of Connecticut Filed May 10, 1965, Ser. No. 454,260 7 Claims. (Cl. 336149) The present invention relates to an autotransformer that is adjustable to provide any one of a plurality of different output voltages. In many applications it has been found desirable to enable selection of a voltage from a plurality of voltages with the. voltages differing by known and sometimes substantially constant increments. One such device which enables the selection has included a transformer having a plurality of taps at which the different voltages appear and a multiple position switch for enabling a user to connect to the tap having the desired voltage. While such a device is operable, it has not been found completely satisf-actory in view of its expense; plurality of components and interconnections and also in view of it generally interrupting the output voltage when the switch is being shifted from one voltage to another.

It is accordingly an object of the present invention to provide an adjustable voltage autotransformer which is capable of providing a plurality of output voltages with each having a dilferent voltage value.

Another object of the present invention is to provide an autotransformer which enables its output voltage to be adjusted in incremental steps with the output voltage being uninterrupted during a change from one step to another.

Y A further object of the present invention is to provide an adjustable voltage autotransformer which achieves the above objects and which is relatively economical to manu- .facture and durable in use.

There is'also connected to the brush, manipulatable means which enables the brush to be moved and which normally urges the brush to be positioned at any one of a plurality of locations. At each location, the brush is in engagement with one of the individual turns to thereby provide the output voltage present at that turn. As the brush is moved between locations, it engages the groups of turns and thus does not interrupt the output voltage during its movement.

A further feature of the present invention resides in the spacing between the group of turns and individual j turns on the commutating path and the width of the .brush. The brush has a width which is less than the distance between adjacent groups of turns but is greater than the distance between an individual turn and a group of turns. Thus the brush when resting on an individual turn only engages the turn and does not bridge two turns.

'With' this construction a number of output voltages may be produced with only a few turns of the winding being I required and also a higher current carrying capacity may be achieved.

' Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is an elevation, partly in section, of an adjustable voltage autotransformer of the present invention.

3,312,921 Patented Apr. 4, 1967 FIG. 2 is an end view thereof.

FIG. 3 is a section taken on the line 3-3 of FIG. 1.

FIG. 4 is an electrical schematic diagram of the autotransforrner of the present invention.

Referring to the drawing, the adjustable voltage autotransformer of the present invention is generally indicated by the reference numeral 10 and is shown secured in an aperture 11 of a panel 12 though if desired it may be con tained Within its own casing to provide a covered unit. The autotransformer in the specific embodiment shown includes an annular core 13 which may be formed by spirally winding a sheet of paramagnetic iron into a substantially annular shape and a winding 14 is wound toroidally on the core with appropriate insulation being provided but not shown herein.

The winding 14 consists of a single length of insulated conducting wire and is wound on the core in a manner that forms individual turns 14a and groups of turns 14b. Each of the groups, as herein shown, consists of three turns, though if desired a greater or lesser number may be employed. A flattened section is formed on a corresponding portion of all of the turns with the flattened portions being substantially planar and forming a commutating surface on which a brush 15 rides to effect electrical engagement with the turn or turns engaged thereby. The brush 15 is preferably of the graphitic type and is mounted in a spring urged holder 16 carried by a disk-shaped metallic member 17. The member 17 is secured on a shaftlS but insulated therefrom by means of an insulating tube 19 and a cylindrical member 29.

The shaft 18 extends through the axis of the core 13 to project through the aperture 11 and is rotatably mountof the knob 21 rotates the shaft 18 which in turn rotatably moves the brush on the commutating surface.

In carrying out the present invention it is desired in the specific embodiment shown to provide a plurality of different output voltages with the same voltage increment therebetween though, as will be hereinafter appreciated,

the voltage increment between different output voltages may be varied. For each output voltage, the brush is urged to a position where it rests only on the individual turn producing the desired value of output voltage and does not engage any other turn. Accordingly there is provided on the disk-shaped member and a flange 20a of the cylindrical member 20, a pair of spring urged plungers 24 and a pair of balls 25. The balls 25 are positioned in openings in the flange 20a and are seatable in spherical segment-shaped depressions 26. The depressions are evenly circularly formedin a substantially annular plate 27 having an extension 28 that is secured as by a screw 29 to the core.

On the other side of the plate 27 there is provided a resiliently bowed washer 30 and a C-r-ing 31 positioned in a groove 32 formed in the cylindrical member 20. The

other end of the member 20 is also formed with a groove 33 in which is positioned another C-was'her 34, the latter abutting a washer 35 which forms a stop for springs 36 located within apertures 37 formed in the disk-shaped p} member 17.

It will thus be appreciated that upon rotation of the knob 21 the balls tend to seat themselves within oppositely disposed depressions 26 and resist movement therefrom. Thus a user when operating the knob is caused to sense the seating of the balls within the depressions. As shown in FIG. 3, the depressions 26 are spaced in axial alignment with individual turns-14a and thus the brush is urged by the balls seating themselves within the depressions to be in radial alignment with an individual turn to thereby be in electrical engagement with an individual turn.

Referring to FIG. 3, a group of turns 14 -is spaced from an adjacent group of turns by an angle indicated by the arrow 38. Each individual turn is spaced an angular distance, indicated by the arrow 39, from an adjacent group'of turns. The brush moreover has a width which is less than the angular distance between adjacent groups of turns but is greater than the angular distance between one turn and its adjacent group of adjacent turns. While the brush as shown herein has a trapezoidal cross-section and hence surface that engages the commutating surface, it will be appreciated that such a configuration is required in view of the winding being toroidal with the inner spacing of the turns being closer than the outer spacing. It will be understood that in the embodiment shown the brush is incapable, when located at any one of its positions determined by the depressions 26, of engaging any other turn but the individual turn on which it is disposed. When the brush is initially moved from one individual turn to another to adjust the output voltage, the brush engages a turn of an adjacent group of turns while maintaining engagement with its individual turn. Further movement of the brush disconnects the brush from the individual turn but maintains contact with at least one turn of the group. Also it engages an individual turn prior to disengagement from the last turn of a group of turns. Thus the brush during its movement continually maintains an output voltage by being in engagement with at least one turn.

The winding 14 has a pair of input terminals 40 and 41 connectible to a source of alternating current and an output terminal that structurally is the extension 28. Currentis conducted from the brush 15 through the spring urged holder 16, the disk-shaped member 17, the cylindrical member and thence to the engagement existing between the annular plate 27 and the cylindrical member 20 and the washer 31. The output voltage accordingly ggpears between the input terminal 41 and the extension It will be understood that by having the brush positioned in electrical engagement with just one turn to produce the desired output voltage, that there is no cir culating current produced as it would be if it bridged two turns and hence the autotransformer may have a larger current carrying capacity. Moreover, though the brush does bridge turns during movement, it is only for a short duration and thus limitations on the autotransformer design as to normal maximum volts per turn may be exceeded. This enables lesser turns to be used in the winding and/ or the use of larger diameter wire having greater current carrying capacity thanin the usual infinitely adjustable voltage autotransformer.

In the embodiment shown, it is desired to have a constant increment difference between adjacent. output voltage locations. Thus each group of turns has the same number of turns. If desired, the groups could have different numbers of turns which would provide different increments of voltages between adjacent positions.

It will accordingly be appreciated that there has been disclosed an adjustable voltage autotransformer which has a movable brush which may be positioned, on a commutating surface formed on a winding at any one of a plurality of locations. The brush. is urged to be at rest at the selected location by resilient means and not be positioned between locations. At each location, the brush is engageable with only a single turn of a winding and thus the winding has a plurality of single turns spaced about the commutating surface with each single turn being aligned with a location. Between each single turn there is a group of turns and the output voltage at each individual turn is dependent not only on the input voltage but also on the number of turns in the group. The groups ofturns and the individual turns are spaced with respect to the brush thickness so that the brush is always engageable with at least one turn thereby preventing any interruption of the output voltage duringmovement of the brush from one location to another.

Variations and modifications may be made within the scope of the claims. and portions of the improvements may be used without others.

We claim:

1. An adjustable voltage autotransformer for providing an output voltage that is adjustable in substantially constant increments comprising a paramagnetic core, a winding wound on said core, input means connected to said winding and adapted to be connected to a source of alternating current, said winding alternately having a group of closely spaced turns and an individual turn, a commutating surface formed on the turns of the winding, said surface of the individual turn being spaced substantially from the surfaces of the groups of turns adjacent thereto, a brush mounted for movement on the commutating surface in electrical engagement therewith and output means connected to the brush and input means.

2. An adjustable voltage autotransformer for providing an output voltage that is adjustable in substantially constant increments comprising a paramagnetic core, a winding wound on said core, input means connected to said winding and adapted to be connected to a source of alternating current, said Winding alternately having a group of closely spaced turns and an individual turn, a

commutating surface formed on the turns of the winding, said surface of the individual turn being spaced substantially from the surfaces of the groups of turns adjacent thereto, a brush mounted for movement on the commutating surface in electrical engagement therewith, means for releasably urging the brush to be located at any one of a plurality of positions, each of said positions aligning the brush with an individual turn and output means connected to the brush and input means.

3. The invention as defined in claim 2 in which the means for releasably urging the brush includes a member having a plurality of depressions located in alignment with the positions, a shaft mounted for rotation, means I mounting the brush on the shaft, seating means carried by the shaft for normally seating in a depression and spring means for urging said seating means into a depres sion but permitting movement out of a depression to another depression.

4. The invention as defined in claim 3 in which the seat-ing means includes at least one ball and the depressions are formed to mate with a portion of said ball.

5. An adjustable voltage autotransformer for providing an output voltage that is adjustable in substantially constant increments comprising a paramagnetic core, a winding wound on said core, input means connected to said winding and adapted to be connected to a source of alternating current, said winding alternately having a group of closely spaced turns and an individual turn, a commutating surface formed on the turns of the winding, said surface of the individual turn being spaced substantially from the surfaces of the groups of turns adjacent thereto, a brush mounted for movement on the commutating surface in electrical engagement therewith, said brush having a width less than the distance on the commutating surface between adjacent groups and greater than the distance between an individual turn and its adjacent group of turns whereby said brush is always in contact withat least one turn and output means connected to the brush and input means.

6. The invention as defined in claim 5 in which each group of turns has the same number of turns thereby providing a substantially constant increment of voltage difference between each position.

7. An adjustable voltage autotransformer for providing an output voltage that is adjustable in substantially constant increments comprising a paramagnetic core, a

winding wound on said core, input means connected to said winding and adapted to be connected to a source of alternating current, said winding alternately having a group of closely spaced turns and an individual turn, a commutating surface formed on the turns of the winding, said surface of the individual turn being spaced substantially from the surfaces of the groups of turns adjacent thereto, a brush mounted for movement on the commutating surface in electrical engagement therewith, means for releasably urging the brush to be located at any one of a plurality of positions, each of said positions aligning the brush with an individual turn, said brush 6 having a width less than the distance on the commutating surface between adjacent groups and greater than the distance between an individual turn and its adjacent group of turns whereby said brush is always in contact with at least one turn and output means connected to the brush and input means.

No references cited.

LEWIS H. MYERS, Primary Examiner. H. W. COLLINS, Assistant Examiner. 

1. AN ADJUSTABLE VOLTAGE AUTOTRANSFORMER FOR PROVIDING AN OUTPUT VOLTAGE THAT IS ADJUSTABLE IN SUBSTANTIALLY CONSTANT INCREMENTS COMPRISING A PARAMAGNETIC CORE, A WINDING WOUND ON SAID CORE, INPUT MEANS CONNECTED TO SAID WINDING AND ADAPTED TO BE CONNECTED TO A SOURCE OF ALTERNATING CURRENT, SAID WINDING ALTERNATELY HAVING A GROUP OF CLOSELY SPACED TURNS AND AN INDIVIDUAL TURN, A COMMUTATING SURFACE FORMED ON THE TURNS OF THE WINDING, SAID SURFACE OF THE INDIVIDUAL TURN BEING SPACED SUBSTANTIALLY FROM THE SURFACES OF THE GROUPS OF TURNS ADJACENT THERETO, A BRUSH MOUNTED FOR MOVEMENT ON THE COMMUTATING SURFACE IN ELECTRICAL ENGAGEMENT THEREWITH AND OUTPUT MEANS CONNECTED TO THE BRUSH AND INPUT MEANS. 